Bug 35513 - Improve targetm.binds_local_p
Summary: Improve targetm.binds_local_p
Status: UNCONFIRMED
Alias: None
Product: gcc
Classification: Unclassified
Component: tree-optimization (show other bugs)
Version: 4.4.0
: P3 normal
Target Milestone: ---
Assignee: Not yet assigned to anyone
URL:
Keywords: missed-optimization
Depends on:
Blocks: 35501 37611 32219 35402 35494
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Reported: 2008-03-09 15:06 UTC by H.J. Lu
Modified: 2022-03-01 15:45 UTC (History)
2 users (show)

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Known to fail:
Last reconfirmed:


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Description H.J. Lu 2008-03-09 15:06:36 UTC
Compiler wants to know:

1. If a symbol will be referenced locally within the file. If a readonly
symbol with initializer is referenced with the file, compiler may
replace symbol read with its initializer. PRs 35402/35494/35501.
2. If a symbol will be referenced locally within the module, an optimized
relocation may be used, depend on symbol types. But for weak, undefined,
hidden function symbol, it is necessary to treat it as global for read.
PR 32219.
3. If a function will be called with in the module, an optimized
relocation may be used.

However, the current targetm.binds_local_p doesn't distinguish those
different usages. As the result, gcc makes wrong conclusions in some
cases, PR 32219.

I think targetm.binds_local_p should take a parameter to indicate
its usage.
Comment 1 H.J. Lu 2008-03-09 15:16:19 UTC
We can add a parameter to indicate for read, write and branch.
Comment 2 H.J. Lu 2010-01-06 23:33:55 UTC
Function pointer != function address in shared library.
When a function is protected, the one defined in shared library
will be called. But its function pointer can be outside of
shared library. So protected function pointer should be
treated as global.
Comment 3 H.J. Lu 2018-01-11 17:22:50 UTC
Hidden ifunc address has the similar issue, see the testcase in PR 83782.
If targetm.binds_local_p needs to know if the symbol is used for read,
write or branch, so that all function pointers, including hidden ones, are
treated as as global, when -fPIC is used.
Comment 4 H.J. Lu 2018-01-11 17:23:18 UTC
*** Bug 83782 has been marked as a duplicate of this bug. ***
Comment 5 CVS Commits 2022-02-09 12:39:22 UTC
The master branch has been updated by H.J. Lu <hjl@gcc.gnu.org>:

https://gcc.gnu.org/g:ab0b5fbfe90168d2e470aefb19e0cf31526290bc

commit r12-7126-gab0b5fbfe90168d2e470aefb19e0cf31526290bc
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Sat Jun 19 05:12:48 2021 -0700

    x86: Add -m[no-]direct-extern-access
    
    Add -m[no-]direct-extern-access and nodirect_extern_access attribute.
    -mdirect-extern-access is the default.  With nodirect_extern_access
    attribute, GOT is always used to access undefined data and function
    symbols with nodirect_extern_access attribute, including in PIE and
    non-PIE.  With -mno-direct-extern-access:
    
    1. Always use GOT to access undefined data and function symbols,
       including in PIE and non-PIE.  These will avoid copy relocations
       in executables.  This is compatible with existing executables and
       shared libraries.
    2. In executable and shared library, bind symbols with the STV_PROTECTED
       visibility locally:
       a. The address of data symbol is the address of data body.
       b. For systems without function descriptor, the function pointer is
          the address of function body.
       c. The resulting shared libraries may not be incompatible with
          executables which have copy relocations on protected symbols or
          use executable PLT entries as function addresses for protected
          functions in shared libraries.
    3. Update asm_preferred_eh_data_format to select PC relative EH encoding
    format with -mno-direct-extern-access to avoid copy relocation.
    4. Add ix86_reloc_rw_mask for TARGET_ASM_RELOC_RW_MASK to avoid copy
    relocation with -mno-direct-extern-access.
    
    gcc/
    
            PR target/35513
            PR target/100593
            * config/i386/gnu-property.cc: Include "i386-protos.h".
            (file_end_indicate_exec_stack_and_gnu_property): Generate
            a GNU_PROPERTY_1_NEEDED note for -mno-direct-extern-access or
            nodirect_extern_access attribute.
            * config/i386/i386-options.cc
            (handle_nodirect_extern_access_attribute): New function.
            (ix86_attribute_table): Add nodirect_extern_access attribute.
            * config/i386/i386-protos.h (ix86_force_load_from_GOT_p): Add a
            bool argument.
            (ix86_has_no_direct_extern_access): New.
            * config/i386/i386.cc (ix86_has_no_direct_extern_access): New.
            (ix86_force_load_from_GOT_p): Add a bool argument to indicate
            call operand.  Force non-call load from GOT for
            -mno-direct-extern-access or nodirect_extern_access attribute.
            (legitimate_pic_address_disp_p): Avoid copy relocation in PIE
            for -mno-direct-extern-access or nodirect_extern_access attribute.
            (ix86_print_operand): Pass true to ix86_force_load_from_GOT_p
            for call operand.
            (asm_preferred_eh_data_format): Use PC-relative format for
            -mno-direct-extern-access to avoid copy relocation.  Check
            ptr_mode instead of TARGET_64BIT when selecting DW_EH_PE_sdata4.
            (ix86_binds_local_p): Set ix86_has_no_direct_extern_access to
            true for -mno-direct-extern-access or nodirect_extern_access
            attribute.  Don't treat protected data as extern and avoid copy
            relocation on common symbol with -mno-direct-extern-access or
            nodirect_extern_access attribute.
            (ix86_reloc_rw_mask): New to avoid copy relocation for
            -mno-direct-extern-access.
            (TARGET_ASM_RELOC_RW_MASK): New.
            * config/i386/i386.opt: Add -mdirect-extern-access.
            * doc/extend.texi: Document nodirect_extern_access attribute.
            * doc/invoke.texi: Document -m[no-]direct-extern-access.
    
    gcc/testsuite/
    
            PR target/35513
            PR target/100593
            * g++.target/i386/pr35513-1.C: New file.
            * g++.target/i386/pr35513-2.C: Likewise.
            * gcc.target/i386/pr35513-1a.c: Likewise.
            * gcc.target/i386/pr35513-1b.c: Likewise.
            * gcc.target/i386/pr35513-2a.c: Likewise.
            * gcc.target/i386/pr35513-2b.c: Likewise.
            * gcc.target/i386/pr35513-3a.c: Likewise.
            * gcc.target/i386/pr35513-3b.c: Likewise.
            * gcc.target/i386/pr35513-4a.c: Likewise.
            * gcc.target/i386/pr35513-4b.c: Likewise.
            * gcc.target/i386/pr35513-5a.c: Likewise.
            * gcc.target/i386/pr35513-5b.c: Likewise.
            * gcc.target/i386/pr35513-6a.c: Likewise.
            * gcc.target/i386/pr35513-6b.c: Likewise.
            * gcc.target/i386/pr35513-7a.c: Likewise.
            * gcc.target/i386/pr35513-7b.c: Likewise.
            * gcc.target/i386/pr35513-8.c: Likewise.
            * gcc.target/i386/pr35513-9a.c: Likewise.
            * gcc.target/i386/pr35513-9b.c: Likewise.
            * gcc.target/i386/pr35513-10a.c: Likewise.
            * gcc.target/i386/pr35513-10b.c: Likewise.
            * gcc.target/i386/pr35513-11a.c: Likewise.
            * gcc.target/i386/pr35513-11b.c: Likewise.
            * gcc.target/i386/pr35513-12a.c: Likewise.
            * gcc.target/i386/pr35513-12b.c: Likewise.
Comment 6 CVS Commits 2022-02-12 13:50:20 UTC
The master branch has been updated by H.J. Lu <hjl@gcc.gnu.org>:

https://gcc.gnu.org/g:5c4258d7c78a92ab17c14dec1163d87fc42ff019

commit r12-7213-g5c4258d7c78a92ab17c14dec1163d87fc42ff019
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Feb 10 05:42:49 2022 -0800

    x86: Update PR 35513 tests
    
    1. Require linker with GNU_PROPERTY_1_NEEDED support for PR 35513
    run-time tests.
    2. Compile pr35513-8.c to scan assembly code.
    
            PR testsuite/104481
            * g++.target/i386/pr35513-1.C: Require property_1_needed target.
            * g++.target/i386/pr35513-2.C: Likewise.
            * gcc.target/i386/pr35513-8.c: Change to compile.
            * lib/target-supports.exp (check_compile): Support assembly code.
            (check_effective_target_property_1_needed): New proc.
Comment 7 CVS Commits 2022-03-01 15:45:48 UTC
The master branch has been updated by H.J. Lu <hjl@gcc.gnu.org>:

https://gcc.gnu.org/g:673a10aee1aafe0c99bfadc29a7458339bdddb3a

commit r12-7436-g673a10aee1aafe0c99bfadc29a7458339bdddb3a
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Tue Mar 1 07:39:33 2022 -0800

    x86: Limit PR 35513 tests to Linux
    
    Limit PR 35513 tests to Linux since they fail on 32-bit Solaris/x86 with
    Solaris linker.
    
            PR testsuite/104725
            * g++.target/i386/pr35513-1.C: Limit to Linux.
            * g++.target/i386/pr35513-2.C: Likewise.